Recently, data carriers such as contactless IC cards, which are capable of transmitting and receiving data while receiving power supply at the same time by using a semiconductor integrated circuit to which power is supplied via electromagnetic waves of a predetermined wavelength utilizing the mutual induction between coils, have reached the stage of practical application. Contactless IC cards are classified into the close-coupled type, the proximity type and the vicinity type based on the reading range between the contactless IC card and the reader/writer, which is a device for exchanging radio waves with the contactless IC card. The standard specification for each type is being fully prepared.
Particularly, proximity type contactless IC cards, which can be used over a distance of up to about 10 [cm] from the reader/writer, are often used in applications such as train passes, with which the ticket gate can be opened and closed based on the contactless exchange of information with the reader/writer, wherein the users do not need to take their train passes (contactless IC cards) out of the train pass holders at the ticket gate, or the like. Thus, contactless IC cards and information systems (contactless type information systems) using the same can potentially be used in a very wide variety of applications.
When data is returned from a contactless IC card to a reader/writer, for example, in such a contactless type information system, the load of a magnetically-coupled coil (antenna coil) of the contactless IC card is varied to modulate the signal (data), thus realizing the return of data.
In a contactless type information system, if the voltage caused by the mutual induction between coils drops when exchanging data due to, for example, the physical distance between the contactless IC card and the reader/writer being excessive, it may disable communications between the contactless IC card and the reader/writer. Therefore, conventional contactless IC cards ensure accurate data communications by resetting the internal semiconductor integrated circuit when the power supply voltage becomes lower than a predetermined reset detection lower limit voltage. (See, for example, Patent Document 1.)
Patent Document 1: Japanese Laid-Open Patent Publication No. 8-77318